The present application is related to co-filed application Ser. No. 10/273,459 filed on an even date herewith entitled xe2x80x9cA Method and Structure for Phased Array Antenna Interconnectxe2x80x9d invented by John C. Mather, Christina M. Conway, and James B. West. The co-filed application is incorporated by reference herein in its entirety. All applications are assigned to the assignee of the present application.
This invention relates to antennas, phased array antennas, and specifically to a construction approach for a phased array antenna.
Phased array antennas offer significant system level performance enhancement for advanced communications, data link, radar, and SATCOM systems. The ability to rapidly scan the radiation pattern of the array allows the realization of multi-mode operation, LPI/LPD (low probability of intercept and detection), and A/J (antijam) capabilities. One of the major challenges in phased array design is to provide a cost effective and environmentally robust interconnect and construction scheme for the phased array assembly.
It is well known within the art that the operation of a phased array is approximated to the first order as the product of the array factor and the radiation element pattern as shown in Equation 1 for a linear array 10 of FIG. 1.                                           E            A                    ⁡                      (            θ            )                          ≡                                                            E                p                            ⁡                              (                                  θ                  ,                  φ                                )                                                    ⏟                              Radinition                ⁢                                  
                                ⁢                Element                ⁢                                  
                                ⁢                Pattern                                              ⁢                                                    [                                                      exp                    ⁡                                          (                                              -                                                  j                                                                                    2                              ⁢                                                              π                                0                                                                                      λ                                                                                              )                                                                            r                    o                                                  ]                                            ⏟                                  Isotropic                  ⁢                                      
                                    ⁢                  Element                  ⁢                                      
                                    ⁢                  Pattern                                                      ·                                                            ∑                  N                                ⁢                                  xe2x80x83                                ⁢                                                      A                    n                                    ⁢                                      exp                    ⁡                                          [                                                                        -                                                      j                                                                                          2                                ⁢                                π                                                            λ                                                                                                      ⁢                        n                        ⁢                                                  xe2x80x83                                                ⁢                        Δ                        ⁢                                                  xe2x80x83                                                ⁢                                                  x                          ⁡                                                      (                                                                                          sin                                ⁢                                                                  xe2x80x83                                                                ⁢                                θ                                                            -                                                              sin                                ⁢                                                                  xe2x80x83                                                                ⁢                                                                  θ                                  0                                                                                                                      )                                                                                              ]                                                                                                  ⏟                                  Array                  ⁢                                      xe2x80x83                                    ⁢                  Factor                                                                                        Equation        ⁢                  xe2x80x83                ⁢        1            
Standard spherical coordinates are used in Equation 1 and xcex8 is the scan angle referenced to bore sight of the array 10. Introducing phase shift at all radiating elements 15 within the array 10 changes the argument of the array factor exponential term in Equation 1, which in turns steers the main beam from its nominal position. Phase shifters are RF devices or circuits that provide the required variation in electrical phase. Array element spacing, xcex94x or xcex94y of FIG. 1, is related to the operating wavelength and it sets the scan performance of the array 10. All radiating element patterns are assumed to be identical for the ideal case where mutual coupling between elements does not exist. The array factor describes the performance of an array 10 of isotropic radiators 15 arranged in a prescribed grid as shown in FIG. 1 for a two-dimensional rectangular array grid 10.
To prevent beam squinting as a function of frequency, broadband phased arrays utilize true time delay (TTD) devices rather than phase shifters to steer the antenna beam. Expressions similar to Equation 1 for the TTD beam steering case are readily available in the literature.
The isotropic radiation element 15 in FIG. 1 has infinitesimal dimensions, as explained in subsequent paragraphs. The spacing of the isotropic radiators 15 determines the scan performance of the phased array 10. The elements 15 must be spaced less than or equal to one half wavelength (xcexo/2) apart for the radiated pattern to be free from grating lobes. Grating lobes are false undesired beams having strength equal to the main beam. The wider the element spacing, xcex94x or xcex94y, the smaller the grating lobe-free scan volume is for the array 10. Array factors are also available for 2-D and 3-D phased arrays having rectangular and hexagonal grid arrangements, but they are not discussed here for the sake of brevity.
The isotropic radiating element 15 is an infinitesimally small, nonphysical mathematical concept that is useful for array analysis purposes. However, all operational arrays utilize physical radiating elements 25 of finite size as shown in the array 20 of FIG. 2. Radiating element size in the plane of a planar array, or along the array surface for a conformal array, is usually a large fraction of xcexo/2, as required for efficient radiation. Since the array spacing, xcex94x or xcex94y, sets the grating lobe-free scan volume of the array 20, it also puts restrictions on the transverse size of the individual radiating elements 25 within the array 20. The extremities of neighboring radiating elements 25 are frequently very close to one another and in some cases, the array spacing, xcex94x or xcex94y, prevents certain types of radiating elements 25 from being used.
A comparison of FIGS. 1 and 2 illustrates how real, physical radiating elements 25 consume the majority of the surface area around the array grid intersection points. The array element spacing, xcex94x or xcex94y, and transverse size restrictions are further exacerbated in electronically scanned phased arrays. The most general two-dimensional, or three-dimensional (arbitrarily curved surface) electrically scanned phased array antennas require phase shifters at each radiating element 25 to electronically scan the main beam of the radiation pattern. A very space-efficient interconnect cable assembly is required to provide the proper control signals, bias and chassis ground to each individual radiating element 25 and the phase shifters (not shown). However, the physical size of the cabling assembly is often too large and cumbersome to effectively route around the array radiating elements 25 without perturbing the RF field of the radiating element 25 and/or the aggregate field of the sub-array or top-level array assemblies.
The referenced application effectively resolves the phased array interconnect problem by utilizing fine pitch, high-density circuitry in a thin self-shielding multi-layer printed wiring assembly. The new approach utilizes the thickness dimension of an array aperture wall (parallel to bore sight axis) to provide the surface area and volume required to implement all of the conductive traces for phase shifter bias, ground, and control lines. The thickness of the printed wiring assemblies 35 are now in the x-y plane (front view) of the radiating elements 25 in the phased array 30 as shown in FIG. 3.
A packaging, interconnect, and construction approach is needed to create a cost-effective EMXT (electromagnetic crystal)-based phased array antennas having multiple active radiating elements in an X-by-Y configuration. EMXT devices are also known in the art as tunable photonic band gap (PBG) and tunable electromagnetic band gap (EBG) substrates. A detailed description of a waveguide section with tunable EBG phase shifter technologies is available in a paper by J. A. Higgins et al. xe2x80x9cCharacteristics of Ka Band Waveguide using Electromagnetic Crystal Sidewallsxe2x80x9d 2002 IEEE MTT-S International Microwave Symposium, Seattle, Wash., June 2002. Each element is comprised of EMXT sidewalls and a conductive (metallic) floor and ceiling. Each EMXT device requires a bias voltage plus a ground connection in order to control the phase shift for each element of the antenna by modulating the sidewall impedance of the waveguide. By controlling phase shift performance of the elements, the beam of the antenna can be formed and steered. The maximum permitted distance between centerlines of adjacent apertures is xcexo/2 in both the X and Y directions and the total thickness of the EMXT plus mounting structure and interconnect must be minimized.
A design approach is needed that utilizes the interconnect scheme disclosed in the referenced application to construct a phased array antenna that can be assembled into a configuration with multiple radiating elements.
A phased array antenna for steering a radiated beam and having an egg crate-like array structure of array elements is disclosed. The phased array antenna is constructed from row slats formed from a metallic substrate. The row slats have a plurality of row slots. Column slats with a plurality of column slots that engage the row slots on the row slats to form the egg crate-like array structure. The column slats are formed from column strips that are configured in a U-shape. Each column strip is configured such that a left side of the U-shape forms a left-hand side of each array element in a column and a right side of the U forms an opposing right-hand side of each array element. Column strip sides are mounted back-to-back with sides of adjacent column strips to form the column slats. The column strip left-hand side is a mirror image of the right-hand side.
The U-shape column strip includes interconnect circuitry and EMXT devices mounted on the U-shape column strip and connected to the interconnect circuitry for shifting phase to steer the radiated beam of the EMXT-based phased array antenna. The EMXT devices mounted to the column strip form left and right sidewalls of each array element. Circuit devices for operation of the phased array antenna are mounted to the U-shaped column strip. A connector is mounted at an apex of the U-shaped column slat.
It is an object of the present invention to create a cost effective improved interconnect and construction approach for an EMXT-based phased array antenna.
It is an object of the present invention to create a phased array antenna capable of having hundreds or thousands of array elements easily fabricated and interconnected either through sub array or direct array construction techniques.
It is an advantage of the present invention to incorporate a fine pitch, high density interconnect scheme to interconnect EMXT phase shifting devices.
It is a feature of the present invention to provide an enhanced construction technique that allows simplified mounting of circuit components to control the phased array antenna.